1) Field of the Invention
This invention pertains to waste processing and, more particularly, to an apparatus and method for removing silver from spent photographic solutions.
2) Description of the Prior Art
The chemistry associated with x-ray photography is well known. Film is coated with a silver emulsion, such as silver halide, which is exposed to x-ray energy. The exposed portion of the emulsion converts to metallic silver. The film is developed by treating it with an alkaline solution that makes the silver more visible. Thereafter, a fixer or photographic solution, which includes ammonium thiosulfate, is applied to the film that dissolves and carries away the silver emulsion that is not converted to metallic silver. The spent fixer contains significant amounts of silver.
It is common practice to recover silver in the fixer solution by replacing the silver ions with iron ions. Generally, this is accomplished by providing electric energy to the spent fixer solution to facilitate the iron transfer. Alternatively, non-electrical type systems have been developed, such as disclosed in U.S. Pat. No. 5,229,009. Under Environmental Protection Agency (EPA) guidelines, the silver content of the spent fixer must be below a certain value before the fixer can be discharged into a sewer. Although electric arrangements can operate satisfactorily, they are expensive to purchase and expensive to operate. The non-electric arrangements are very limited on the volume of spent solution that can be processed and, in many cases, cannot meet the EPA discharge values. This results in subsequent processing of the spent photographic solution before it can be discharged into a sewer.
Therefore, it is an object of the present invention to provide a non-electric silver reclamation system for spent photographic solution that effectively removes silver from the photographic solution so that the solution can be disposed of in a sewer.